In the repair of hydraulic components of a hydrostatic system, it is often necessary to clean the components of such a system because of contamination from dirt and water. Typically, a system of this type includes a fluid reservoir, and a source of contamination of the system is the air vent on the reservoir itself. This vent allows dirt and water to enter the system and mix with the hydraulic fluid in the reservoir, thereby contaminating the fluid and requiring the fluid to be filtered to a major extent to prevent breakdown of the system because of contamination. Thus, because of this contamination problem, a need has continued to exist for some time for improvements in the handling of hydraulic fluids for driving hydraulic motors and other components of a hydrostatic system so that such fluids will not become contaminated and thereby require frequent repair and cleaning so as to minimize interruptions in the operation of the system. The present invention satisfies this need.